Cardiovascular disease (CVD) remains the number 1 killer of women in the United States (US). Importantly, CVD mortality of African American women exceeds that of white women and although the rates of CVD mortality are declining overall in men and women, they are declining most slowly in African American women. As the US population ages and lives longer the incidence of CVD will become a disproportionately greater problem for African American women. The explanation for ethnic differences in CVD risk is multifactorial and complex with insufficiency of vitamin D providing a provocative and testable hypothesis as a possible link between CVD risk factors (particularly hypertension in African Americans) and increased risk of atherosclerosis in African Americans. The possibility of a causal link between vitamin D deficiency and CVD is supported by many studies as well as strong biological plausibility. Given the aging population and rapidly increasing incidence of obesity, vitamin D insufficiency is becoming an increasingly important public health issue that may contribute to CVD. This may be particularly relevant for African American women, who are at particular risk for CVD since increased skin pigmentation reduces the capacity of skin to synthesize vitamin D and due to decreased bioavailability of vitamin D in obesity, which disproportionately affects African American women. Although data suggest a possible beneficial effect of vitamin D supplementation in reducing CVD, a direct anti- atherogenic effect from randomized controlled trials is limited. The goal of this proposal is to integrate an ancillary stuy of atherosclerosis imaging into the parent trial, Vitamin D and Osteoporosis Prevention in Elderly African Americans, a 4-year, randomized, double-blind, placebo-controlled study designed to investigate the effect of vitamin D status in elderly African American women. 250 African American women >65 years old with serum 25-hydroxyvitamin D (25(OH)D) levels greater than 20 nmol/L but less than 65 nmol/L will be randomized to sufficient vitamin D3 supplementation once daily to raise serum 25(OH)D levels to between 75 nmol/L and 172 nmol/L versus placebo. The effect of vitamin D3 supplementation on the progression of subclinical carotid artery atherosclerosis measured as the rate of change of common carotid artery (CCA) intima-media thickness (IMT) and change of CCA stiffness (distensibility, elasticity and compliance) in computer image processed B-mode ultrasonograms will be determined. This ancillary study provides the opportunity to cost-effectively address whether vitamin D supplementation reduces the progression of atherosclerosis, specifically in an understudied unique cohort of elderly African American women. PUBLIC HEALTH RELEVANCE: Given the aging population and rapidly increasing incidence of obesity, vitamin D insufficiency is becoming an increasingly important public health issue that may contribute to cardiovascular disease (CVD). This may be particularly relevant for African American women, who are at particular risk for CVD since increased skin pigmentation reduces the capacity of skin to synthesize vitamin D and due to decreased bioavailability of vitamin D in obesity, which disproportionately affects African American women. This ancillary study to Vitamin D and Osteoporosis Prevention in Elderly African Americans will cost-effectively address whether vitamin D supplementation reduces the progression of atherosclerosis, specifically in an understudied unique cohort of elderly African American women.